1. Field of the Invention
The present invention relates to bearings that are resiliently mounted to an outer shell to optimize load capacity for varying operating conditions. More specifically, the present invention relates to bearings for precisely supporting a shaft for axial and rotational motion under various temperature, load, wear, and tolerance conditions.
2. Description of Related Art
Conventional bearings which are used to support a shaft during axial and rotational notion have inwardly extending bearing pads that are designed to deform slightly under loading in order to optimize formation of a converging hydrodynamic wedge that corrects for any shaft,misalignment. However, shaft misalignment may also occur at low load forces prior to the wedge formation in conventional hydrodynamic bearings (for example, when the shaft is rotating at a low angular velocity.)
Conventional bearing designs address the problems associated with high revolution per minute rotational shaft motion, yet do not address problems associated with high precision linear (axial) or rotational motion at low to medium speeds. Also, hydrodynamic bearings rely on lubrication such as air, oil or grease to form the hydrodynamic wedge.
Linear ball bearings specifically designed for high precision axial motion are expensive and may be cost prohibitive in many situations. Also less expensive standard sleeve bearings do not achieve a contact fit due to the tolerance build up of the shaft, housing, and the bearing itself. In both instances, a minimum clearance between the shaft and bearing is required for assembly and temperature compensation. This clearance condition will allow the shaft to move slightly within the bearing, thereby reducing the precision of the bearing.
Consequently, there is a need for a bearing that is capable of maintaining axial alignment of the shaft at low to medium axial and rotational speeds. The bearing should be capable of maintaining axial aligment of the shaft by adjusting in response to temperature. The bearing should be capable of maintaining a contact fit with the shaft despite the tolerance ranges of the shaft and the bearing and despite wearing of the bearing over time. The bearing should have stable bearing pads and good overall structural integrity. The bearing should also be capable of operating efficiently without the use of lubrication such as air, oil, or grease.
Some examples of various types of bearings that have been designed to support a rotating shaft are referenced as follows: U.S. Pat. No. 5,549,392 issued on Aug. 27, 1996, to William J. Anderson; U.S. Pat. No. 5,531,524 issued on Jul. 2, 1996, to Douglas J. Brouwer; U.S. Pat. No. 5,205,652 issued on Apr. 27, 1993, to William I. Chapman; U.S. Pat. No. 4,790,372, issued on Dec. 13, 1988, to Steven R. Komplin; U.S. Pat. No. 4,743,125 issued on May 10, 1988, to Uwe Dammel et al.; U.S. Pat. No. 4,671,678 issued on Jun. 9, 1987, to Gunter Munch; U.S. Pat. No. 4,600,317 issued on Jul. 15, 1986, to Sanae Mori; U. K. Patent Application No. 2,273,746(A) published on Jun. 29, 1994; German Patent Application No. 3,544,392(A1) published on Jun. 19, 1987; U. K. Patent Application No. 1,517,160 published on Jul. 12, 1978; and U. K. Patent Application No. 1,458,047 published on Dec. 8, 1976. The above listed patents and patent publications do not solve the aforementioned problems as does the present invention.
U.S. Pat. No. 5,664,888 issued on Sep. 9, 1997 to Jeffrey M. Sabin describes zero clearance bearings which have an outer shell supporting three cantilevered arcuate bearing pads on fingers. These bearings are distinguishable from the present invention because (1) no temperature consideration was disclosed; (2) the cantilevered structure of the bearing pads do not suggest the present beam structure on outside legs; (3) the calculations for a simply supported beam of the present invention are different for a cantilevered bearing pad of the zero clearance bearing; and (4) the present inventive structure supports twice as much load as the cantilevered bearing pad on a finger.
U.S. Pat. No. 5,489,155 issued on Feb. 6, 1996, U.S. Pat. No. 5,284,392 issued on Feb. 8, 1994, U.S. Pat. No. 5,222,815 issued on Jun. 29, 1993, U.S. Pat. No. 5,215,385 issued on Jun. 1, 1993, and U.S. Pat. No. 5,112,143 issued on May 12, 1992, to Russell D. Ide describe bearings that include a plurality of circumferentially spaced bearing pads supported by various configurations of support members. These patents do not teach a bearing capable of maintaining axial alignment of the shaft by adjusting in response to temperature. These patents neither have the same stability in the bearing pads nor the same structural integrity in the outer shell as does the present invention.
U.S. Pat. No. 5,033,871 issued on Jul. 23, 1991, to Russell D. Ide describes an extrudable hydrodynamic bearing constructed entirely of non-newtonian fluidic materials or composites thereof. This patent does not teach a bearing capable of maintaining axial alignment of the shaft by adjusting in response to temperature.
U.S. Pat. No. 4,627,746 issued on Dec. 9, 1986, to Charles H. Grisel et al. describes a hydrodynamic fluid bearing assembly constituted by bearing members disposed around a rotary shaft with the interposition of a film of pressurized fluid. At least one of the members is subject to the action of a resilient member generating a limited pre-load force in order to maintain the assembly in its correct interrelationship when the shaft is stationary. The patent to Grisel et al. does not teach a bearing capable of maintaining axial alignment of the shaft by adjusting in response to temperature.
U.S. Pat. No. 3,980,352 issued on Sep. 14, 1976, to Jerome A. Carlson describes a spring bearing assembly comprising a bearing member (continuous or discontinuous) positioned between an inner race surface and an outer race surface. The bearing member is urged into constant positive contact with the race surfaces by internal bearing spring forces. The assembly is distinguishable by having internal and external races enclosing a spring tensioned bearing member.
U.S. Pat. No. 4,714,357 issued on Dec. 22, 1987, to Ronald W. Groth et al. describes a segmental bearing shoe for use in segmental bearings that rotably support a member by means of a plurality of bearing shoes. The device is distinguishable for its segmental structure.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, a temperature compensated bearing solving the aforementioned problems is desired.